Saving Materials to be a texture
In the first place you have to make a proper UV map of your object, this is a very basic and well known practice which will guarantee to you that whenever you open your model again (in every almost format) the textures will cover the correct faces of it.

The second thing that you have to take a look is Baking Textures (both in cycles and blender internal the procedure is similar but not the same).

After creating your UV maps and setting your material you will bake the render passes you need (you may not need baking shadows for instance) in separate files or merge them (one beauty pass) all of them in one single file.

These two steps are what are you mainly looking for, you will find a bunch of tutorials on youtube, on how to create UV maps (one or multiple - depending your needs after you understand the concept) and then baking the different render passes in textures.

The "Bake" panel is a place to start from